The present invention relates to a process for the preparation of fluorinated benzene sulfonyl fluorides.
The conversion of aryl sulfonyl chlorides or bromides to the corresponding aryl halide proceeds in good yield upon the action of light as taught by Miller et al., "The Displacement of Aromatic Substituents by Halogen Atoms," J. Am. Chem. Soc. 79, 4187 (1957); metallic catalysts as taught by U.S. Pat. No. 3,256,343 and Blum et al., "Desulfonylation of Aromatic Sulfonyl Halides Catalyzed by Some Platinum-Metal Complexes," J. Org. Chem. 35(6), 1895 (1970); or potassium chloride as taught by Yakobson et al., "Aromatic Fluorine Derivatives, XXIV Fluorine-Containing Benzenesulfonyl Fluorides," J. Gen. Chem. USSR Eng. Trans. 37, 149 (1967). Similar conditions for the conversion of aryl sulfonyl fluorides fail entirely or give poor yields.
Consequently, while the conversion of aryl sulfonyl fluorides to aryl fluorides is known, the reaction is not generally reported as being synthetically useful. For example, U.S. Pat. No. 3,256,343 reports the formation of fluorobenzene in 31% yield by passing benzenesulfonyl fluoride over copper on charcoal at 360.degree. C. Blum et al., supra, report the formation of 2-fluoronaphthalene in 10% yield from 2-naphthalenesulfonyl fluoride in the presence of RhCl(PPh.sub.3).sub.3 as catalyst. Yakobson et al., supra, report the formation of fluorobenzene in 10% yield from benzenesulfonyl fluoride by reacting with potassium fluoride and state that replacement of a sulfonyl chloride group by chlorine under the action of potassium chloride occurs more readily than the replacement of a sulfonyl fluoride group by fluorine under the action of potassium fluoride.
Ortho- and/or para-fluorinated aryl sulfonyl fluorides are prepared by methods such as fluorine-chlorine exchange reactions on chlorobenzenesulfonyl chlorides or fluorides as taught by U.S. Pat. No. 4,369,145. This method is limited in that chlorine which is meta to a halosulfonyl group may exchange only with difficulty; this is a common situation in aromatic substitution reactions in which the leaving group is meta to the activating group.
Fluorinated aryl sulfonyl fluorides are also prepared by the reaction of fluorobenzenes with chlorosulfonic acid as taught by Gilbert, "Sulfonation and Related Reactions," Interscience, New York, 1965, p. 84-87 or the decomposition of a fluorinated aryl diazonium salt in the presence of sulfur dioxide and hydrogen chloride as taught by Meerwein et al, Chem. Ber. 90, 841 (1957), followed by conversion of the fluorinated aryl sulfonyl chloride to fluorinated aryl sulfonyl fluoride. These methods are also limited in that they require expensive fluorobenzene precursors and sulfonation generally occurs para to fluorine, unless another more powerful directing group is present, which may not be desired.
It would be desirable to have an easier process for the preparation of fluorinated benzene sulfonyl fluorides wherein the yield is good and the reactants are less expensive than the reactants required by known processes.